Schneider Optics Split-Field Diopters. 138mm, allows more of the scene to be in total focus simultaneously and are often used to increase depth of field in pictures shot with anamorphic lenses. These filters produce a shot with deep focus, where objects near and far into focus.

Since split focus diopters are half convex glass, when attached to your camera's lens, it makes one side nearsighted, and the other farsighted. What this allows you to do is focus on multiple planes -- you could have objects in the foreground and background completely in focus. This also means that the staging of your scene must be well-prepared.